"We only use something like 10 percent of our brain, anywhere between 5 and 15 percent—I don't know what the current estimates are," as vos Savant told the reference book Newsmakers. In her view, humans are capable of much more. But motivation is the key: "So how much of a role is motivation playing day-to-day, when we are talking about much smaller differences? And is it measuring, perhaps—this is just a wild, out-of-the-blue kind of a guess— does it measure one person using 17.7 percent of their brain versus some one person who uses 17.8 percent? Is that what I.Q. does? I doubt it. But it's one of those things where personality—or whatever you might call it—plays a great role, and I happen to have [it]. "